RESUMO
In renal hypertensive rats the cerebral concentration of alpha-methyldopa, alpha-methyldopamine, alpha-methylnoradrenaline, dopamine and noradrenaline as well as the blood-pressure were determined simultaneously. The antihypertensive effect followed a time course identical to that of the increase in the cerebral concentration of alpha-methyldopamine and of the decrease in the concentration of dopamine, whereas lowering of blood pressure on the one hand, and changes in the levels of alpha-methylnoradrenaline and noradrenaline, on the other, were not related to each other. Dose-response relationships showed the same correlations and lack of correlations, respectively. These results suggest that non-betat-hydroxylated catecholamines play a major role in mediating the antihypertensive effect of alpha-methyldopa or, alternatively, that only the newly biosynthesized alpha-methyl-noradrenaline is effective in lowering blood pressure.